Silaborations of Unsaturated Compounds

Abstract: This thesis deals with the development of transition metal-catalyzed silaborations of 1,3-dienes and 1,6-enynes.The first part of the thesis describes the development of the enantioselective 1,4-silaboration of 1,3-cyclohexadiene. A number of chiral metal-ligand complexes were evaluated. Up to 82% enantiomeric excess was obtained using a catalyst system derived from Pt(acac)2 and a phosphoramidite ligand. The product formed was employed in allylborations of aldehydes, giving homo-allylic alcohols in good yields with good to moderate diastereoselectivity. In attempts to widen the scope of silaborations to include acyclic, terminally substituted 1,3-dienes, products from H-B exchange with, and H-Si addition to, the dienes were obtained.The second part describes the development of silaborative carbocyclization of 1,6-enynes. A Pd N-heterocylic carbene complex was found to be effective for the silaborative carbocyclization of unsubstituted enynes, giving the products in good to excellent yields. Employing terminally substituted enynes resulted in low or no yields.The last part describes investigations into the reaction mechanisms of the processes developed in the first part. It was found that the silylborane undergoes oxidative addition to a Pt(0) complex generated from Pt(acac)2 and DIBALH. After insertion of 1,3-cyclohexadiene into the Pt-B bond a π-allyl complex was observed experimentally. In the addition of silylborane to acyclic, terminally substituted, 1,3-dienes it was shown by deuterium labeling experiments that one diene loses a hydride via H-B exchange and that this hydride is then added to another diene via H-Si addition. A reaction mechanism was proposed for this process.